Recovery of ortho-xylene



Patented Oct. 19, 1943 UNIT ED .STAT PAT-EN 'RECQVERY or oRTHo-XYLENE T Peroy 'J. lCole, flhladelphia; Pa.,y assignor, by

mesne assignments, Corporation Y No 'Drawing'.

to AlliedzChemical & Dye

@monitrice-toter1111941,

invention is directed "tofqa process forthcrecovery `of vjorthoyl'ene"irorrl oils kcontaining vit 'and .lleboilinjgjolens and `other like-boiling. non-#aromatic hydrocarbons, (e. 5g.. naphthenes .or pararll-n's.4 j

Ortho-xylene is present in oil fractions 'such as oil and .fractionsrecoveredirom :cracked petroleum products. .By .dripoilVI-areier .tothose .condensates from .carburetted water :gas such-as .oondensates formed inthe .gas .disimibuting` @lines or holders or the light oil which :hercondcnsed-infoooling thecarburetted `Water gas after l removal of tar. .Drip oilsy may vcontain about .5%

ortho-.xylene; .li common..characteristic of. ,drip oils and, cracked'j petroleum products. .is 'thatin 'addition to' fthe arornalthydrooarbons `they ,conf ta'in'a substantial proportion o'f like-boiling, `nonparomatl'c hydrocarbons including goleiins andV par;-` aiiins'orinaplfrthenes.`y `i j vDim-Lilla'tion of/*drip ,oil .or oracked,.petroleum products emcient'rectifcation ofthe vapors may be employed to .recover-a ractionin vwhich the ortho-xylen'e is concentrated. However. even with efficient "rectification ajfraction containing `more *thanabout ;80% *to V85% ortho-.Xylene can rarely 'be obtained., `Oleiins together with' para'mns and vusual-1y some naphthenes and traces of metajparafxylene maker/inthe remaining ii5% to 20% of 'the ortho-xylen'e `fraction. Ifhese non-'aromatici hydrocarbons ,individually j may have boiling points ranging *from considerably vLbelow :to v*above the Iboilingpoint of ortho-'xylena e. fg. their `boiling lpoints 'may rangefrom A1 00"V to '155 C., whereas ortho-Xylene .boils 'at about 1511i? C. Nevertheless, these :non-'aromatics vcannot be caribous. I

yhemcal treatment ofoils such asreferredto above "has been used kto recover pure orthoxylene therefrom, but such methodsfhavehitherto been cumbersome and expensive. f

I have now discovered that a pure `ortho-Xylene may recovered from an' oil containingfittogether with like-'boiling fole'fins and other 'non-f aromatic vhvcfirocarbons (parans,ornaphthenesil by .subjecting the oil lto a Series ,0I three-treat-4 ments,` "I 'have' 'discovered that bychlorinating the ,oil "the relative ",volatilities Iof thel'a'rornatic hydrocarbon and/other constituents ofthe oil may be so'changedwith respect Ato ea'chDlilflBr that. .bv iractipnallvdstllins. the chlorinatedoil the. .non-aromatic Ahydrocarbon constituents "can be selectively removedl to ang- .exten t not possible Prior tochlvrin'ation., I have icondthatgthjre.- mainderoi the. likeboiling,,non-aromatic hydro; carbons may- 'be separated from. the l'aroriaticfbi azeotrnpicniyfdistiuing the on, either `prior t its chlorination ory afterjthe fractional distillation of the "chlorinated oil. While it sjpossible lto@ re)- 'tivelypur'efortho-Xylene 'product by `the'foregoingr 'combination of steps irrespectivevoi Whether-fthe 'azeotrpic' distillation precedes or follows `the steps ofnchlor'inetionand www distillation, have discovered' that the aroma-'tic 'hydrocarbon may lvbe'st 'berecc'ivered inhigh yields'and of high @mehr-.first ze'tropieally dsiillri-g theolfffac tion andi-,hereafter chlorinating the re due offthe azeotropi lstmatitngjand rractiarfauy ois-billing, -tirefschiqrmatefd residue. Y

*it is preferred that 'the i aromatic -oii l'fraction to from whiohfcons'titents boilingyironithe oil ra? tionY` at temperatures lhig-her and lower' thanf the desired ortho-Xylene '-boilsfthereffrom have l'been removed. *For y*exalr'nrilin 'recovering ortho;

xyiene'lnom'drip oil-it ispr'eferreo tof-nrs@ nac@ Ation-ally distill and was'h`- concentratei'r sul# furie' acid A"the drip" oil -n'difftoeeover there:

from j a close Eclit `'ffraction "which the ortho- Xy1ene is concentrated, such vasr 'a' 'fraction boiling' in thefrange 135? fC. to' 1215?'1-fe. Less advanta'geously the indstral, "acid-Washed 'X'ylol irac'f tions boilingin theA range 1 -35', CQ to 155 `C'., or Xylene oils of, even broader boiling range, may be inggrangesL- Q'Inuthe,i treatment 'ofi oilsloritaining Xylene,r libe-boiling, non.- aromatic'"hydrocarbonsV y lectiteiyseparafa 'from the :igiene bythe'emo:

rination and ,distillation treatments `asdescribed above, When'low boiling constitnentsa present inthe oil' subjected 'tothe azeotropicf distillation;

nonearomatic hydrocarbons: "'*High* boilingr conincreases the burden upon the equipment ern ployed for this distillation.

commercial ortho-xylene concentrate had the following characteristics:

Specific gravity at 15.5 C 0.862 Melting point 31 C. Francis Bromine No 0.119 Distillation range 92% distilling at 143-144.1 C.

This ortho-xylene fraction was obtained from drip oil by fractionally dstilling the drip oil,

f taking off that fraction in which the ortho-Xylene For the azeotropic distillation of the ortho'- f xylene fraction I prefer to employ methanol as.

the azeotropic agent. My invention is not limited, however, to the use of particular azeotropic agents. with non-aromatic hydrocarbons boiling from ther oil fraction in the same temperature range as the ortho-xylene boils therefrom may be employed. .Among the numerous materials which maybe used are the following: an aliphatic monohydroxyalcohol containing 1 to 5 carbon atoms to the molecule (methanol, ethari'oLetcJ;` monomethyl ether of ethylene glycol, pyridine or allyl alcohol. l y e' I `In the azeotropic distillation the ortho-Xylene is left in the residue `separate from like-boiling parafns and naphthenes which are distilled over as azeotropes with theV methanol orother agent used. [A portion of the'oleiins is likewise carried over in the distillate. The residue of this distillation` contains the orthoxylene.and like-boiling oleflns. It may also contain a residual small i amount of paraflins or naphthenes not completely separated fromthe oil by the azeotropic distillation. -f f I Y g The oil residue of the azeotropic distillationis then chlorinated, preferably by passing chlorine gas into the oil until the oil turns yellow. The change of color to yellow takes place rather suddenly vas the chlorineis bubbled into the oil and is a` good indication thatsuiiicient chlorine has reacted with the oil for treatment by the next step of my process. Although I prefer to'rtreat the oil with chlorine gas, other chlorinating materials may be employed such aschlorine water o r other materialwhich will yield free chlorlnefor combination with hydrocarbons present. Iprefer to chlorinate the oil at ordinary room temperatures, although somewhat higher or lower temperatures may be, employed. Excessively high temperatures should be` avoided, however. sincethey may cause undesirable reactions of chlorine with the oil.

The chlorinated oil is subjected to fractional distillation. Hydrochloric acid present in the oil is neutralized with an alkali before subjecting the oil to fractional distillation. It is also preferred to have present in the fractional distillation an alkali, such as sodium carbonate, to neutralize any hydrochloric acid formed during the` fractional distillation. In this distillation the fraction of the distillate containing the relatively pure aromatic hydrocarbon is collected separate from the forerunnings and higherV boiling materials, the latter 'of which may be left as a residue of the distillationwhen the aromatic hydrocarbon has been taken over and collected separate vfrom the lower boiling materials.

The following eiamples are illustrative of the use of myinvention for the treatment of particular oil fractions to recover theY aromatic hydrocarbon contained thereinzr,4 v v Y Example 1.-A particularly pure, acid-washed,

Any material known to formazeotropes Was concentrated and Washing this fraction with concentrated sulfuric acid. This is a conventional procedure heretofore followed for the recovery of concentrated ortho-xylene products from drip oil.

,This ortho-xylene fraction was mixed with methanol in the proportions of 400 volumes of methanol for every volumes of the orthoxylene fraction. The mixture was then subjected to afractional distillation. In the presence of the methanol the non-aromatics of thexylene fraction were in large part selectively distilled over as azeotropes leaving behind a residue which, after washing with water, had the following char7 act-eristics:

Specific gravity at 15.5 VC

Melting point '-27' C. Francis Bromine `No s 0.104 0rtho-xylene 9293%bylweight Distillation range t i r i Y.

VV87%distilling at 138.8144.7 C. Chlorinewas bubbled'through the residue of theazeotropic distillation until the residue Aturned Yellow. The chlorinated'residue Wasneutralized with a 10% caustic ,sodamsolutin and the neutralized oil separated from the aqueoussolution. This oil was then fractionally distilledin the presence of a small lamount of sodium carbonate. Distillation started with the`vapors at'the top of the fractionation column `in which the vapors were rectified at 136.4" C. When 20% ofthe oil had been distilled over and the temperatureof the vapors at the topl of the rectification column was at 144.3" C.,`the succeeding distillate was collected separately from the preceding forerunnings. The distillation was continueduntil 70% of the oil had been distilled overand the vapor temperature at the topof the rectification column was 144.4a C. Towards the .end ofthe distillation of the chlorinated residue to take over this ortho-xylene fraction, some hydrochloric acid .was formed and not neutralized by the sodium carbonate initially added to the material being distilled. The distillate coming over containing this hydrochloric acid was Washed with caustic soda solution to remove this hydrochloric acid. .T he distillate collected as described, sepa; rate from forerunnings and higher boiling ma? terials `left as residue, was a substantially pure ortho-xylene with a melting point 25.5 to 25 C., a Bromine'No.V 0.003 and .arefractive index (Ndy 20) 15047-15048 By fractionally distilling'the abovefchlorinated distillate under a reduced pressure of,100 mm. Hg, a fraction with a melting point of substanj tially 25.5 C. and consisting of substantially pure ortho-xylene maybe obtained.` However, the yield and purity of the ortho-xylene product are not as satisfactory as when the distillation is carried out at substantiallyatmospheric press sure.

Eample 2.-'1he oil fraction ofExample 1 containing,80% to 83%l ortho-xylene was first chlorinated `bubbling chlorine-through the .oil fraction it ftumedtllnw. `'Bhe chlorinated Noil was neutralized mithacausticnoda isolutioniand the inentralized oil l"fractionally :distilled in the presence of sodium carbonate. Distillaiiion 4started. mith-the "-.wapors 4at ythe.itopd .fthe fractionation :column: usedifor :rectifyingA fthe vapors fat i143.;8?=.(3 ,Aidisiiiltate representing 510% of the .oil charged l'was fcollected'ruvithrsthe temperature Vof "thexyapors at 4the itop'sof the'ifractionation .'.columnrrising .to Lf 'This' distillate was ymixed with twice iits nol'ume of :methanol `and "the .mixture ractinnally @distilled f .Non-aromaticfhydrocarhons lwere azeotropically ,distilledaoyer :with

por temperature at the top of the column reached 140 C. the distillation was stopped. The residue was treated with chlorine gas until it turned yellow. chlorination of the oil residue was checked by determining the Bromine No. of the chlorinated oil. With the Bromine No.'0.003 or less (grams of bromine absorbed per gram of oil), the ychlorination was sufliciently complete for the subsequent steps of the process.

The chlorinated oil was washed with a 20% caustic soda solution to neutralize it and the ywashed oil was fractionally distilled in the presence of a small amount of sodium carbonate. Distillation started with the vapors at the top of the lfractionation column at 144.0 C. The vapor temperature gradually rose to 144.2 C. The melting point of the initial distillate was 27.2 C. and as the distillation progressed the melting point of the distillate rose to 25.3 C., leaving a residue with a melting point below 30 C. By collecting separately from the forerunnings those cuts with melting points of 25.5 C. to 25.3 C., a substantially pure ortho-xylene product was obtained.

As an explanation of the reason for thev above described pro-cess serving to recover the aromatic hydrocarbon separate from like-boiling, non-aromatic hydrocarbons, the following is offered. By the azeotropic distillation like-boiling parains and naphthenes are largely separated from the aromatic hydrocarbon, together with a portion of the like-boiling olens. In chlorinating the cil, free chlorine reacts preferentially with the olens to form therewith addition products. By this chlorination the distillation temperatures of the several constituents of the oil relative to one another, including the relative distillation temperatures of the aromatic hydrocarbon and small amounts of parainic and naphthenic hydrocarbons which may be present, are so altered that upon fractional distillation of the chlorinated oil the aromatic hydrocarbon may be taken over in a fraction, separate from forerunnings and higher boiling materials, which is substantially free from materials other than the aromatic hydrocarbon.

f' 'ilihe' herein described process fior 'the :recovery -of orthoaxylenef products fromoils icontaining ortho-.xylene ltogether. f iwith like-.boiling .olens fand other likeiboilln'gnv mon-aromatic hydrocar- Ibons :is :particularlyiixnportant zbecause heretofore no :economical method'ihas been known `'for :the recovery of '.pure :ortho-xylene 'from Lsuo'h roils. -Wliile :pure :toluene and benzene may be' .obtained from certain drip oil fractions by washingthe .oil Awith]concentratedisulfuric acidandracltionalfly :distilling tliewashed .'material, 'thisiprocess .'is vnot :satisfactory iwhen applied rtothe recovery of `ortho-f-.rxylene :from `-drip vnil concentra-tes. 'The recoveryof :ortho-xylene from drip presents .a uniquezproblem .andtths specicpailplicationfof .fmy invention :is of -particularimportance A,becrnlse .it provides an :economical method forzthegrecoyery .ofthe ortho-xylene.- l n .Theterm folefins;is -used .in this `.specification :and l inthe appended claims fin-abroad sense'fto `include 'unsaturated -hydrocarbonsg ,fhaving one .double .bond .-in :the molecule or lha:\ii1i g ra .higher -degreeoi iunsaturation,l-,e; g. diolens v iiclaim: f y w "The .preesskforiihe recovery offertho xylene from a sulfuric acid-washed oil containing the saine and containing like-boiling olens and other like-boiling, non-aromatic hydrocarbons formed by the high temperature decomposition of petroleum oil, which comprises subjecting said acid-Washed oil to a series of three treatments comprising an azeotropic fractional distillation whereby like-boiling, non-aromatichydrocarbons are selectively removed from a residue containing said aromatic hydrocarbon, a,l chlorination treatment whereby oleiinsr are converted into chlorinated hydrocarbons, andy anon-azeotropic fractional distillationof the chlorinatedv mate'- rial, and in that fractional `distillation to which the oil is last subjected in carrying out the aforedescribed series of steps, recoveringan'orthoxylene having a melting point above 25.8 C. substantially completelyseparated from the nonaromatic hydrocarbons in said acid-Washed oil. 2. The process for the recovery of ortho-xylene from a sulfuric acid-Washed drip oil fraction containing the same together with like-boiling, non-aromatic hydrocarbons including like-boiling olenswhich comprises subjecting said oil to a'series of three treatments comprising an azeotropic fractional distillation whereby likeboiling, non-aromatic hydrocarbons are selectively removed from a residue containing orthoxylene, a chlorination treatment wherebyolens are converted into chlorinated hydrocarbons, and a non-azeotropic fractional distillation of the chlorinated material, and in that fractional distillation to which the oil is last subjected in carrying out the aioredescribed series of steps recovering an ortho-xylene. having a melting point above 25.8 C. substantially completely separated from the non-aromatic hydrocarbons in said acid-Washed oil.

3. The process for the recovery of ortho-xylene from asulfuric acid-washed drip oilfraction containing ortho-Xylene and like-boiling, non-aromatic hydrocarbons, including like-boiling olens, which comprises rst azeotropically distilling said drip oil fraction in the presence of a material which forms low boiling azeotropes with non-aromatic hydrocarbons present in the oil and. thereby selectively separating from said ortho-xylene like-boiling, non-aromatic hydro'` carbons present in said oil, including a portion of the like-boiling olens, as a distillate leaving a residue lcontaining `ortho-Xylene and. like-boil'- ing ,o1efins, lchlorinating said residue, fractionally distilling thechlorinated residue and collectingas distillate a fractionhaving a melting point no lower than 25.5 C. which substantially consists of ortho-xylene separate from forerunnings and the higher boiling materials present in the chlorinated oil residue subjected to the fractional distillation. v s i 4. The process for the'recovery of ortho-xylene from a sulfuric acid-Washed drip oil Vfraction containing ortho-xylene and like-boiling, nonarornatlc hydrocarbons, including like-boiling oleflns, which comprises first azeotropically distilling said .drip oil fraction in the presence of methanol and thereby selectively separating from said ortho-Xylene likeboilin'g, non-aromatic hydrocarbons present in said oily-including a. portion' of the like-boiling olefins, as a' distillate leaving an oil residue containing orthoxylene and like-boiling oleiins, treating said oil residue with gaseous chlorine'until the oil residue develops a yellow color, fractionally distilling the chlorinated oil residue and collecting as distillatea fractionhavirlg-arneltingA point no lower than -25.5C. which substantially consists of ortho-Xylene separate from forerunnings and the higher boiling materials present in the chlorinated oil residus subjected to the fractional distillation.

5. The process for the recovery of ortho-xylene from a sulfuric acid-Washed oil containing the same and containing like-boiling olefins and other like-boiling, non-aromatic hydrocarbons, which comprises subjecting said acid-washed oil to a series of three treatments comprising an azeotrcpic fractional distillation whereby likeboiling, non-aromatic hydrocarbons are selectively removed from a residue containing said aromatic hydrocarbon, a chlorination treatment whereby olefins are converted into chlorinated hydrocarbons, and a non-azeotropic fractional distillation of the chlorinated material, and in that fractional distillation to which the oil is last subjected in carrying out the aforedescribed series of steps, recovering an ortho-xylene having a melting point above 25.8 C. substantially completely separated from non-aromatics in the oil subjected to this distillation.

PERCY J. COLE. 

